In a transformer, the instantaneous voltage induced across the secondary coil is given from Faraday's Law by:Vs=NsdΦ/dt where Ns is the number of turns in the coil and Φ is the magnetic flux. (integral of magnetic field over the cross-sectional area of the coil) If the coil axis is perpendicular to the magnetic field lines, (normally the case by choice in transformers) total flux reduces to a product of the flux density B and the (constant) area A through which it cuts. B varies with time according to the excitation of the primary. By Gauss's law for magnetism the same magnetic flux passes through both the primary and secondary coils so in an ideal transformer the instantaneous voltage across the primary winding is:Vp=NpdΦ/dt Therefore the voltages, turns ratios and currents in the two coils can be related by:Vs/Vp=Ns/Np=Ip/Is Many applications of prior art transformers follow these equations, as illustrated in FIG. 1.